1. Field of Invention
The present invention relates to an ink composition for ink jet recording and particularly concerns an ink composition suitable for (i) ink jet recording processes in in which the ink is jetted by a rapid decrease in the inner volume of an ink container or by extrusion or suction from an ink container under a definite externally applied pressure; (ii) an ink jet recording process in which the ink is electrostatically accelerated across a potential difference created by a signal applied between a nozzle and the counter electrode of the printer; or (iii) an ink mist recording process in which an ink mist is generated using ultrasonic vibration.
2. Description of the State of the Art
The following characteristics are required of an ink employed in the above-described ink jet or ink mist processes.
(i) that the ink have a density sufficiently high to record clear dark images,
(ii) that the ink not stop up the jet nozzle,
(iii) that the ink not change in its physical properties or give rise to precipitates (coagulate) upon storage, and
(iv) that the ink be capable of producing records which are not smeared or removed when wetted with water or perspiration.
The addition of dyes in a high concentration to various sorts of conventionally prepared hydrophobic inks is difficult, because the addition is accompanied by an increase in viscosity of the ink and, even if solvents of low viscosity are used to dissolve the dyes, the dyes tend to separate out as the low viscosity solvents evaporate. Too high a viscosity and formation of dye precipitates are fatal defects in an ink to be used in an ink jet recording process wherein the ink is forced (jetted) through a fine nozzle.